Transmitting and receiving system, transmitting apparatus, transmitting method, receiving apparatus, receiving method, and program

ABSTRACT

A transmitting and receiving system is provided. The transmitting of receiving system includes a transmitting apparatus to transmit data and a receiving apparatus to receive the data by means of radio communication. The transmitting apparatus includes: data transmission means for transmitting the data; state information reception means for receiving state information indicative of states of the radio communication from the receiving apparatus; and control means for controlling transmission using the data transmission means. When the state information reception means receives state information indicating a degraded state of the radio communication, the control means stores control information for the data transmission means to control transmission immediately before the state information is received; and, when the state information reception means thereafter receives state information indicating a normal state of the radio communication, the control means uses the most recently stored control information to control transmission by means of the data transmission means. The receiving apparatus includes: data reception means for receiving data transmitted from the data transmission means by means of the radio communication; determination means for determining the radio communication state based on data received by the data reception means; and state information transmission means for transmitting state information indicating the radio communication state determined by the determination means to the transmitting apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Japanese Patent ApplicationNo. 2005-122971 filed in the Japanese Patent Office on Apr. 20, 2005,the entire contents of which being incorporated herein by reference.

BACKGROUND

The present application relates to a transmitting and receiving system,a transmitting apparatus, a transmitting method, a receiving apparatus,a receiving method, and a program. More specifically, the applicationrelates to a transmitting and receiving system, a transmittingapparatus, a transmitting method, a receiving apparatus, a receivingmethod, and a program capable of fast resuming data transmission qualityduring recovery from a degraded state to a normal state based on atransmission control state before the degradation in consideration forradio variations and radio link control.

In due course of progress in the recent home networking and increasingneed for radio communications (e.g., cellular network, radio LAN (LocalArea Network), and UWB (Ultra Wide Band)), there is expected anincreasing demand for streaming reproduction of high-quality audiovisualdata via radio networks in the future.

In an expected situation, for example, a user may want to usebidirectional communication services such as video on-demand servicesand video chatting supplied by a content provider. The user may want tostreamingly reproduce data transmitted from the content provider on apersonal computer (PC) or a display unit wirelessly connected to thecontent provider at home.

Transmission of data on IP (Interlace Progressive) networks requirescontrol over transmission rates in accordance with states of datareproduction encoding rates, available bands on the IP network, and IPnetwork congestion. General techniques for controlling transmissionrates include not only the technique using TCP (Transmission ControlProtocol) having data arrival reliability, but also the technique usingRTP (Real-time Transport Protocol) defined in highly realtime RFC(Request For Comment) 1889 (e.g., TFRC (TCP-Friendly Rate Control)defined in RFC3448). These techniques are constructed to aim at wirednetworks with small communication errors.

Generally, a radio network uses multiplex transmission lines(multi-paths) due to reflected waves from various obstacles. Accordingto the transmission channel characteristic (communication channelcharacteristic), propagation delay differences cause frequency selectivefading that distorts frequency characteristics within transmission bandsto remarkably vary or degrade communication states (communicationquality).

By contrast, a radio network area is formed between a sending party anda receiving party and is composed of a radio base station and a radioterminal. In order to improve remarkable variations or degradation ofcommunication states, the radio network area is provided with techniques(radio link control) such as antenna diversity, error resistive bitcoding, and error packet retransmission.

Even though these techniques are provided, radio communication states orambient environment degrades communication states such as an increase inpacket error rates (radio packet error rates) or Round Trip Time (RTT)during radio communication for a short or long period of time. Suchdegradation of the communication state is exceptional for theabove-mentioned techniques of controlling wired network transmissionrates. As a result, the degraded communication state causes congestionin the radio communication and degradation or instability of the datatransmission quality (transmission rate (sending rate), transmissiondelay, etc.). After the radio communication state recovers, thetransmission rate recovery delays. Accordingly, the above-mentionedtechniques of controlling wired network transmission rates are improperfor the streaming reproduction.

FIGS. 1A through 1C show examples of indoor experiment on a radio LAN.With reference to these diagrams, the following describes communicationsituations of controlling transmission rates according to thetransmission rate control technique using the RTP operating on the UDP(User Datagram Protocol) under fading environment.

FIG. 1A shows temporal changes of radio packet error rates (%). FIG. 1Bshows temporal changes of transmission rates (Mbps). An upper part ofFIG. 1C shows temporal changes of RTT (ms). A lower part of FIG. 1Cshows temporal changes of loss rates of packets (packet loss rates) (%).In FIGS. 1A through 1C, the abscissa represents time (s).

As shown in FIG. 1A, several states correspond to the radio packet errorrates at the boundary of approximately 20%: a degraded state havinglarge values for a short period, less than several hundreds ofmilliseconds; a degraded state having large values for a long period,ranging from several hundreds of milliseconds to several seconds; and anormal state having small values. The boundary and values indicatespecific tendencies depending on fading situations and radio chipalgorithms.

In FIG. 1A, a high radio packet error rate for one second or longeroccurs approximately at the time point of 42 seconds (circle A1 in FIG.1A) to decrease the corresponding throughput (transmissible effectiverate) for improving the radio network. As shown in FIG. 1C, the RTT andthe packet loss rate increase accordingly (circles C1 and D1 in FIG.1C). As a result, the transmission rate control technique using RTPdecreases the transmission rate as the RTT and the packet loss rateincrease.

Afterwards, as shown in FIG. 1A, approximately at the time point of 44or 45 seconds, the long degrading radio state is restored to the normalstate with a low error rate (point A2 in FIG. 1A). Also in this case, ittakes approximately three or four seconds b1 for the transmission rateto resume a state (point B2 in FIG. 1B) equivalent to the state beforethe degraded radio state. This is because the AIMD (Additive Increase,Multiplicative Decrease) algorithm is used to gradually increase thetransmission rate for recovery.

Similarly, in FIG. 1A, a high radio packet error rate for one second orlonger occurs approximately at the time point of 55 seconds (circle A3in FIG. 1A). As a result, the throughput for the radio area decreases.As shown in FIG. 1C, the RTT and the packet loss rate increaseaccordingly (circles C2 and D2 in FIG. 1C). Also in this case, thetransmission rate decreases as the RTT and the packet loss rate increase(circle B3 in FIG. 1B). The transmission rate remains low approximatelyat the time point of 57 seconds (point A4 in FIG. 1A) where the radiopacket error rate is restored to the normal state. It takesapproximately 10 seconds b2 for the transmission rate to be restored(point B4 in FIG. 1B).

As a result, the transmission rate is controlled based on thetransmission rate control technique using the RTP in FIGS. 1A through1C. Increasing the RTT (points C1 and C2 in FIG. 1C) causes irregularframing in a streamed image. Afterwards, remarkable degradation occurswhen the transmission rate decreases (between points B1 and B2 andbetween points B3 and B4 in FIG. 1B).

As mentioned above, the transmission rate control technique using thePTP causes discrepancy between the transmission rate and the throughputfor the radio area during a long degraded radio state. The RTT and thepacket loss rate increase to remarkably decrease the transmission rate.In addition, the transmission rate slowly recovers after the radio staterecovers. Because of these two factors, that control technique isinappropriate for streaming reproduction.

To solve this problem, there is a demand for a transmission rate controltechnique that has a congestion control function requested for wirednetworks, complies with the above-mentioned transmission channelcharacteristics specific to radio networks and effects of the controlprovided for radio networks, and provides high-performance and stabledata transmission quality.

It is desirable to possibly avoid changes in the existing systemconstruction such as introducing a new apparatus.

For example, a possible transmission rate control technique compliantwith radio networks determines a congestion state and a degraded radiostate based on the RTT, the packet loss rate, and the radio packet errorrate. To correct degraded radio states, there is the technique thatmaintains and stabilizes the transmission rate (e.g., see JP2001/160824).

However, the technique disclosed in JP 2001/160824 gives noconsideration to the radio link control such as the above-mentionedpacket retransmission performed on radio networks, thus causingcongestion during radio communication.

According to the other techniques (e.g., see JP 2004/153616 and JP2004/153619), a radio communication terminal determines the radiocommunication transmission rate using control information such as DRC(Data Rate Control) in the 1xEV-DO cellular packet network system andtransmits the transmission rate to a data delivery apparatus. Thetechniques disclosed in JP 2004/153616 and JP 2004/153619 cannot beapplied to radio LANs that are provided with no protocol fortransmitting control information such as DRC. Further, the techniquesdisclosed in JP 2004/153616 and JP 2004/153619 give no consideration tothe congestion control for wired and radio communications.

According to yet another technique, a relay node on the wired networkconverts data encoding rates depending on degradation of radiocommunication states detected by using the packet loss rate to adjustrates of transmission to the radio base station. In this manner, therelay node prevents a delay in data arrival from increasing. That is,the technique separates the radio communication from the wiredcommunication for control (e.g., see JP 2004/15761).

However, the technique disclosed in JP 2004/15761 uses the packet lossrate to detect degradation of communication states, thus slowing downthe response time of the transmission rate control. The system usingthis technique requires a relay node.

Moreover, JP 2001/160824, JP 2004/153616, JP 2004/153619 and JP2004/15761 provide no control over radio communication states inconsideration for the long-term and short-term states discussed withreference to FIGS. 1A to 1C.

SUMMARY

As disclosed in the above-mentioned related art, there are proposedseveral transmission rate control techniques compliant with radionetworks. However, no techniques provide fast restoration of the datatransmission quality after restoration of the radio state and are suitedfor streaming reproduction.

Embodiments of the present application are able to give consideration toradio state variations and radio link control, decrease degradation ofdata transmission quality when the radio communication is degraded, andfast recover the data transmission quality based on a transmissioncontrol state before degradation when the radio communication recoversfrom a degraded state to a normal state.

In a first transmitting and receiving system according to an embodiment,a transmitting apparatus includes data transmission means fortransmitting data, state information reception means for receiving stateinformation indicative of a radio communication state from a receivingapparatus, and control means for controlling transmission performed bythe data transmission means. When the state information reception meansreceives state information indicating a degraded state of the radiocommunication, the control means stores control information for the datatransmission means to control transmission immediately before the stateinformation is received. When the state information reception meansthereafter receives state information indicating a normal state of theradio communication, the control means uses the most recently storedcontrol information to control transmission by means of the datatransmission means. The receiving apparatus includes: data receptionmeans for receiving data transmitted from the data transmission means bymeans of the radio communication; determination means for determiningthe radio communication state based on data received by the datareception means; and state information transmission means fortransmitting state information indicating the radio communication statedetermined by the determination means to the transmitting apparatus.

A first transmitting apparatus according to an embodiment includes: datatransmission means for transmitting the data; state informationreception means for receiving state information indicative of states ofthe radio communication from the receiving apparatus; and control meansfor controlling transmission using the data transmission means. When thestate information reception means receives state information indicatinga degraded state of the radio communication, the control means storescontrol information for the data transmission means to controltransmission immediately before the state information is received. Whenthe state information reception means thereafter receives stateinformation indicating a normal state of the radio communication, thecontrol means uses the most recently stored control information tocontrol transmission by means of the data transmission means.

The state information reception means receives state informationrepresenting any one of a long degraded state, a short degraded state,and the normal state of the radio communication. When the stateinformation reception means receives state information indicating a longdegraded state of the radio communication, the control means controlstransmission corresponding to a degraded state of the radiocommunication.

The control information includes information about a transmission rateor RTT. When the state information reception means receives stateinformation indicating the degraded state and then state informationindicating the normal state, the control means can control transmissionof the data transmission means so that the data is transmitted at themost recently stored transmission rate or at a transmission ratecalculated using control information including the RTT.

The control information further contains information of Round Trip Time(RTT). When the state information reception means receives stateinformation indicating the degraded state and then state informationindicating the normal state, the control means can control transmissionof the data transmission means so that the data is transmitted at atransmission rate calculated based on the most recently storedtransmission rate and RTT.

A first transmitting method according to an embodiment includes:transmitting the data; receiving state information indicating the radiocommunication state from the receiving apparatus; and controllingtransmission according to a process of the data transmission step. Whena process at the state information reception step receives stateinformation indicating a degraded state of the radio communication, aprocess at the control step stores control information for controllingtransmission according to a process at the data transmission stepimmediately before reception of the state information. When the stateinformation reception step thereafter receives state informationindicating a normal state of the radio communication, the process at thecontrol step uses the most recently stored control information tocontrol transmission according to the process at the data transmissionstep.

A first transmitting program according to an embodiment includes:transmitting the data; receiving state information indicating the radiocommunication state from the receiving apparatus; and controllingtransmission according to a process of the data transmission step. Whena process at the state information reception step receives stateinformation indicating a degraded state of the radio communication, aprocess at the control step stores control information for controllingtransmission according to a process at the data transmission stepimmediately before reception of the state information. When the stateinformation reception step thereafter receives state informationindicating a normal state of the radio communication, the process at thecontrol step uses the most recently stored control information tocontrol transmission according to the process at the data transmissionstep.

A first receiving apparatus according to an embodiment includes: datareception means for receiving data transmitted from the transmittingapparatus by means of the radio communication; determination means fordetermining the radio communication state based on data received by thedata reception means; and state information transmission means fortransmitting state information indicating the radio communication statedetermined by the determination means to the transmitting apparatus.

The determination means can determine based on the received data thatthe radio communication state corresponds to which of a long degradedstate, a short degraded state, and a normal state.

The first receiving apparatus further includes detection means fordetecting radio communication information about the radio communicationstate based on the data. The determination means can determine the radiocommunication state based on a value for the radio communication statedetected by the detection means at a specified time and an average ofvalues for the radio communication information detected within aspecified time period including that time.

A first receiving method according to an embodiment includes the stepsof: receiving data transmitted from the transmitting apparatus by meansof the radio communication; determining the radio communication statebased on data received by a process at the data reception means; andtransmitting state information indicating the radio communication statedetermined by a process at the determination step to the transmittingapparatus.

A second program according to an embodiment includes the steps of:receiving data transmitted from the transmitting apparatus by means ofthe radio communication; determining the radio communication state basedon data received by a process at the data reception means; andtransmitting state information indicating the radio communication statedetermined by a process at the determination step to the transmittingapparatus.

In a second transmitting and receiving system according to anembodiment, a transmitting apparatus includes: data transmission meansfor transmitting the data; control information reception means forreceiving control information to control transmission performed by thedata transmission means; and control means for controlling transmissionperformed by the data transmission means based on control informationreceived by the control information reception means. A receivingapparatus includes: data reception means for receiving data transmittedfrom the data transmission means by means of the radio communication;determination means for determining the radio communication state basedon data received by the data reception means; generation means forgenerating the control information based on the radio communicationstate determined by the determination means; and control informationtransmission means for transmitting control information generated by thegeneration means to the transmitting apparatus. When the determinationmeans determines the radio communication state to be degraded, thegeneration means stores the most recently generated control information.When the determination means thereafter determines the radiocommunication state to be normal, the generation means uses the mostrecently generated control information to generate the controlinformation.

A second transmitting apparatus according to an embodiment includes:data transmission means for transmitting the data; control informationreception means for receiving control information which is transmittedfrom the receiving apparatus based on the radio communication state andis used to control transmission performed by the data transmissionmeans; and control means for controlling transmission performed by thedata transmission means based on control information received by thecontrol information reception means.

A second transmitting method according to an embodiment includes thesteps of: transmitting the data; receiving control information which istransmitted from the receiving apparatus based on the radiocommunication state and is used to control transmission according to aprocess at the data transmission step; and controlling transmissionaccording to a process of the data transmission step based on controlinformation received by a process at the control information receptionstep.

A third program according to an embodiment includes: transmitting thedata; receiving control information which is transmitted from thereceiving apparatus based on the radio communication state and is usedto control transmission according to a process at the data transmissionstep; and controlling transmission according to a process of the datatransmission step based on control information received by a process atthe control information reception step.

A second receiving apparatus according to an embodiment includes: datareception means for receiving data transmitted from the transmittingapparatus by means of the radio communication; determination means fordetermining the radio communication state based on data received by thedata reception means; and generation means for generating controlinformation to control transmission performed by the transmittingapparatus based on the radio communication state determined by thedetermination means; and control information transmission means fortransmitting control information generated by the generation means tothe transmitting apparatus. When the determination means determines theradio communication state to be degraded, the generation means storesthe most recently generated control information. When the determinationmeans thereafter determines the radio communication state to be normal,uses the most recently generated control information to generate thecontrol information.

The determination means determines based on the received data that theradio communication state corresponds to which of a long degraded state,a short degraded state, and the normal state.

When the determination means determines the radio communication state tobe long degraded, the generation means generates the control informationcorresponding to the radio communication state's degraded state.

The second receiving apparatus further includes detection means fordetecting radio communication information about the radio communicationbased on the data. The determination means determines the radiocommunication state based on a value for the radio communication statedetected by the detection means at a specified time and an average ofvalues for the radio communication information detected within aspecified time period including that time.

The control information includes information about transmission rates orinformation of Round Trip Time (RTT). When the determination meansdetermines the radio communication state to be degraded and then to benormal, the generation means generates control information based on themost recently stored control information including transmission rate andRTT.

A second receiving method according to an embodiment includes the stepsof: receiving data transmitted from the transmitting apparatus by meansof the radio communication; determining the radio communication statebased on data received by a process at the data reception means;generating control information to control transmission performed by thetransmitting apparatus based on the radio communication state determinedby a process at the determination step; and transmitting controlinformation generated by a process at the generation step to thetransmitting apparatus. When a process at the determination stepdetermines the radio communication state to be degraded, a process atthe generation step stores the most recently generated controlinformation. When a process at the determination step thereafterdetermines the radio communication state to be normal, a process at thegeneration step uses the most recently generated control information togenerate the control information.

A fourth program according to an embodiment includes the steps of:receiving data transmitted from the transmitting apparatus by means ofthe radio communication; determining the radio communication state basedon data received by a process at the data reception means; generatingcontrol information to control transmission performed by thetransmitting apparatus based on the radio communication state determinedby a process at the determination step; and transmitting controlinformation generated by a process at the generation step to thetransmitting apparatus. When a process at the determination stepdetermines the radio communication state to be degraded, a process atthe generation step stores the most recently generated controlinformation. When a process at the determination step thereafterdetermines the radio communication state to be normal, a process at thegeneration step uses the most recently generated control information togenerate the control information.

When the transmitting apparatus receives state information from thereceiving apparatus, the state information may indicate a degraded stateof the radio communication. In this case, the first transmitting andreceiving system according to an embodiment stores the controlinformation for controlling data transmission immediately before thestate information is received. When the transmitting apparatusthereafter receives state information indicating a normal state of theradio communication, the first transmitting and receiving system usesthe most recently stored control information to control the datatransmission. The receiving apparatus uses the radio communication toreceive data from the transmitting apparatus. Based on the data, thereceiving apparatus determines the radio communication state andtransmits the state information indicating the radio communication stateto the transmitting apparatus.

When the transmitting apparatus receives state information from thereceiving apparatus, the state information may indicate a degraded stateof the radio communication. In this case, the first transmittingapparatus, the first transmitting method, and the first programaccording to an embodiment store the control information for controllingdata transmission immediately before the state information is received.When the transmitting apparatus thereafter receives state informationindicating a normal state of the radio communication, the transmittingand receiving system the first transmitting apparatus, the firsttransmitting method, and the first program use the most recently storedcontrol information to control the data transmission.

The first receiving apparatus, the first receiving method, and thesecond program according to an embodiment receive data transmitted fromthe transmitting apparatus by means of radio communication. Based on thedata, the first receiving apparatus, the first receiving method, and thesecond program determine a radio communication state and transmit stateinformation indicating the radio communication state to the transmittingapparatus.

In the second transmitting and receiving system according to anembodiment, the transmitting apparatus receives control information forcontrolling transmission and controls data transmission based on thecontrol information. The receiving apparatus receives data transmittedfrom the transmitting apparatus by means of radio communication anddetermines a radio communication state based on that data. When theradio communication state is determined to be degraded, the receivingapparatus stores the most recently generated control information. Whenthe radio communication state is thereafter determined to be normal, thereceiving apparatus uses the most recently stored control information togenerate control information and transmits the control information tothe transmitting apparatus.

The second transmitting apparatus, the second transmitting method, andthe third program according to an embodiment receive control informationthat is transmitted from the receiving apparatus based on the radiocommunication state and is used to control data transmission. Based onthe control information, the second transmitting apparatus, the secondtransmitting method, and the third program control the datatransmission.

The second receiving apparatus, the second receiving method, and thefourth program according to an embodiment receives data transmitted fromthe transmitting apparatus by means of radio communication anddetermines a radio communication state based on that data. When theradio communication state is determined to be degraded, the secondreceiving apparatus, the second receiving method, and the fourth programstore the most recently generated control information. When the radiocommunication state is thereafter determined to be normal, the secondreceiving apparatus, the second receiving method, and the fourth programuse the most recently stored control information to generate controlinformation and transmit the control information to the transmittingapparatus.

According to the above described embodiments, it is possible to decreasedegradation of data transmission quality when the radio communication isdegraded, and quickly recover the data transmission quality based on atransmission control state before degradation when the radiocommunication recovers from the degraded state to a normal state.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the present invention will be described in detail basedon the following figures, wherein:

FIGS. 1A to 1C exemplify transmission rates when a well-knowntransmission rate control technique is used to control transmissionrates;

FIG. 2 shows a functional construction example of a transmission systemaccording to an embodiment of the invention;

FIG. 3 is a block diagram exemplifying the hardware construction of atransmitter in FIG. 2;

FIG. 4 describes state s determined by an analysis unit in FIG. 2;

FIG. 5 is a flowchart showing a data reception process performed by areceiving terminal in FIG. 2;

FIG. 6 is a flowchart showing a radio state determination process atStep S6 in FIG. 5;

FIG. 7 is a flowchart showing a transmission rate calculation processperformed by a rate calculation unit in FIG. 2;

FIG. 8 shows a data transmission process in which the transmitter inFIG. 2 transmits data to the receiving terminal;

FIGS. 9A to 9C show transmission rates when the transmission system inFIG. 2 controls transmission rates under fading environment;

FIG. 10 shows another functional construction example of a transmissionsystem according to an embodiment;

FIG. 11 is a flowchart showing a data reception process performed by areceiving terminal in FIG. 10; and

FIG. 12 shows a data transmission process in which a transmitter in FIG.10 transmits data to the receiving terminal.

DETAILED DESCRIPTION

Embodiments of the present invention will be described in further detailbelow with reference to the accompanying drawings.

FIG. 2 shows a functional construction example of a transmission system1 according to an embodiment.

The transmission system 1 in FIG. 2 is composed of a transmitter 11, areceiving terminal 12, a wired IP network 13, and a radio base station14. The transmitter 11 sends (transmits) data to the receiving terminal12 via the IP network 13 and the radio base station 14. The receivingterminal 12 receives the data by means of radio communication. In theappended claims, data transmission means can be embodied by atransmission unit 24A in FIG. 2, for example; state informationreception means can be embodied by a reception means 24B in FIG. 2, forexample; control means can be embodied by a rate calculation unit 25 inFIG. 2, for example; data reception means can be embodied by a receptionmeans 42B in FIG. 2, for example; determination means can be embodied byan analysis unit 47 in FIG. 2, for example; and state informationtransmission means can be embodied by a transmission unit 42A in FIG. 2,for example.

The transmitter 11 is composed of a content storage unit 21, a codingunit 22, a transmission control unit 23, a communication unit 24, a ratecalculation unit 25, a storage unit 26, and a timer unit 27.

The content storage unit 21 of the transmitter 11 stores data previouslytransmitted from an external personal computer (not shown) via the IPnetwork 13. Further, the content storage unit 21 stores data captured bya digital still camera (not shown) provided for the transmitter 11. Thecontent storage unit 21 also reads data stored in the content storageunit 21 and supplies the read data to the coding unit 22.

The coding unit 22 determines a coding rate based on a transmission ratefrom the rate calculation unit 25. Using the coding rate, the codingunit 22 encodes data supplied from the content storage unit 21,packetizes the data, and supplies it to the transmission control unit23. As a result, the data is transmitted at the transmission rate fromthe rate calculation unit 25.

The transmission control unit 23 supplies the communication unit 24 withthe packetized data from the coding unit 22. Each packet is providedwith a sequential number (hereafter referred to as a sequence number)and has header information including the sequence number and the like.

The communication unit 24 is composed of the transmission unit 24A andthe reception means 24B. The transmission unit 24A transmits packetizeddata from the transmission control unit 23 via the IP network 13 and thebase station 14. The reception means 24B receives a control message. Thecontrol message is information representing: radio communication state stransmitted from an antenna 41 via the IP network 13 and the basestation 14; a radio packet error rate; a packet loss rate; a sequencenumber; and time t between the time to receive data (hereafter referredto as a data reception time) on the receiving terminal 12 correspondingto the reception means 24B itself and the time to transmit the controlmessage (hereafter referred to as a control message transmission time)from itself. The reception means 24B supplies the control message to therate calculation unit 25.

The rate calculation unit 25 calculates the transmission rate and theRTT based on the control message from the reception means 24B andinformation indicative of the current time supplied from the timer unit27. Depending on needs, the rate calculation unit 25 supplies thetransmission rate and the RTT to the content storage unit 26 for storageand reads the transmission rate and the RTT already stored in thestorage unit 26. The rate calculation unit 25 supplies the transmissionrate to the coding unit 22.

The coding unit 22 may provide hierarchical coding compliant with JPEG(Joint Photographic Experts Group) 2000. In such case, the ratecalculation unit 25 supplies the transmission control unit 23 with thetransmission rate. The transmission control unit 23 adjusts the amountof data to be transmitted based on the transmission rate to change thetransmission rate.

The storage unit 26 stores the transmission rate and the RTT from therate calculation unit 25. The timer unit 27 keeps track of the currenttime and supplies the information indicative of the current time to therate calculation unit 25.

The IP network 13 is provided for a provider or the inside of a home,for example, and is connected to the base station 14. Data istransmitted from the transmission unit 24A of the communication unit 24and is supplied to the base station 14 via the wired IP network 13. Thebase station 14 receives the control message corresponding to the radiowave. That control message is supplied to the reception means 24B of thetransmitter 11 via the wired IP network 13.

The base station 14 outputs radio waves corresponding to the datasupplied via the IP network 13 and receives output radio waves via theantenna 41 to perform radio communication.

The receiving terminal 12 is composed of the antenna 41, the radiocommunication unit 42, a reception detection unit 43, a decoding unit44, an output unit 45, a radio monitoring unit 46, the analysis unit 47,a storage unit 48, and a timer unit 49.

The base station 14 outputs a radio wave that is received at the antenna41 and is then supplied to the radio communication unit 42. The radiocommunication unit 42 is composed of the transmission unit 42A and thereception means 42B. The analysis unit 47 supplies the transmission unit42A with the control message, i.e., the information indicative of radiocommunication state s, the radio packet error rate, the packet lossrate, the sequence number, and time t. The transmission unit 42Apacketizes the control message and outputs a radio wave corresponding tothe packetized control message via the antenna 41.

The reception means 42B receives the radio wave via the antenna 41 andconverts it into data corresponding to the radio wave. The receptionmeans 42B supplies the data to the reception detection unit 43 and theradio monitoring unit 46. That is, the reception means 42B uses radiocommunication to receive data from the base station 14 via the antenna41 and supplies the received data to the reception detection unit 43 andthe radio monitoring unit 46.

The reception detection unit 43 detects a packet loss rate in the entirecommunication channel (the IP network 13 and the radio area between thebase station 14 and the antenna 41) based on the packetized data fromthe reception means 42B and supplies the packetized data to the analysisunit 47. The reception detection unit 43 acquires a sequence number inthe header information attached to the packet. The reception detectionunit 43 is supplied with the time information indicative of the currenttime from the timer unit 49. Based on the time information, thereception detection unit 43 acquires the current time as data receptiontime. The reception detection unit 43 supplies the sequence number andthe data reception time to the analysis unit 47. Further, the receptiondetection unit 43 supplies the decoding unit 44 with data from thereception means 42B.

The reception detection unit 43 may detect not only the packet lossrate, but also the number of received packets and the RTT.

The decoding unit 44 decodes data from the reception detection unit 43and supplies the data to the output unit 45. The output unit 45 outputsimages and sounds corresponding to the data from the decoding unit 44.

The radio monitoring unit 46 monitors information about radio-specificcommunication states resulting from fading and the like based on thepacketized data from the reception means 42B. For example, the radiomonitoring unit 46 monitors physical errors such as verification errorsand CRC (Cyclic Redundancy Check) errors as the information aboutradio-specific communication states to calculate the radio packet errorrate. The radio monitoring unit 46 supplies the radio packet error rateto the analysis unit 47.

The radio monitoring unit 46 may monitor the information aboutradio-specific communication states including not only the radio packeterror rate, but also received wave intensity, signal-to-noise ratio,communication speed mode, radio bit error rate, and the number ofretransmissions. According to the embodiment, however, the informationrepresents influences (RTT, throughput, etc.) on the communicationchannel due to fading in consideration for experimental measurementsusing a radio LAN. In addition, the embodiment exemplifies a radiopacket error rate the receiving terminal 12 can acquire.

The analysis unit 47 supplies the radio packet error rate from the radiomonitoring unit 46 to the storage unit 48 for storage. The analysis unit47 reads the radio packet error rate already stored in the storage unit48 and determines radio communication state s based on the radio packeterror rate. The analysis unit 47 works based on the time informationfrom the timer unit 49 to identify the time to transmit a controlmessage as the control message transmission time. The analysis unit 47calculates time t between the control message transmission time and thedata reception time from the reception detection unit 43. The analysisunit 47 supplies the control message to the transmission unit 42A of theradio communication unit 42. In this case, the control message containsinformation indicative of state s, the radio packet error rate from theradio monitoring unit 46, the packet loss rate and the sequence numberfrom the reception detection unit 43, and time t.

The storage unit 48 stores the radio packet error rate from the analysisunit 47. The timer unit 49 keeps track of the current time and suppliesthe information indicative of the time to the reception detection unit43 and the analysis unit 47.

FIG. 3 is a block diagram exemplifying the hardware construction of thetransmitter 11 in FIG. 2.

As shown in FIG. 3, a CPU (Central Processing Unit) 61 is connected toROM (Read Only Memory) 62 and RAM (Random Access Memory) 63 via a bus64. The CPU 61 performs various processes in accordance with a programstored in the ROM 62 or a program recorded in a recording unit 68. TheRAM 63 stores programs and data used for the CPU 61 as needed.

Further, the CPU 61 connects with an input/output interface 65 via thebus 64. The input/output interface 65 connects with an input unit 66composed of a keyboard, a mouse, and the like, and an output unit 67composed of an LCD (Liquid Crystal Display), a CRT (Cathode Ray Tube),and the like. The CPU 61 performs various processes corresponding tocommands supplied from the input unit 66. The CPU 61 outputs images andsounds resulting from the processes to the output unit 67.

The recording unit 68 connected to the input/output interface 65 iscomposed of a hard disk, for example, and records programs and variousdata used for the CPU 61. The communication unit 69 communicates withthe receiving terminal 12 via the IP network 13 and the base station 14,for example.

Programs may be acquired via the communication unit 69 and may berecorded in the recording unit 68.

A drive 70 is connected to the input/output interface 65, drives aremovable medium 71 such as a magnetic disk, an optical disk, amagnetic-optical disk, or semiconductor memory when mounted, andacquires programs or data recorded therein. The acquired program or datais transferred to the recording unit 68 for recording.

The receiving terminal 12 is constructed similarly to the transmitter 11and the description is omitted. The communication unit 69 of thereceiving terminal 12 is composed of the antenna 41 and the like toprovide radio communication.

Referring now to FIG. 4, the following describes state s determined bythe analysis unit 47 in FIG. 2.

As shown in FIG. 4, radio communication state s is represented as threelevels 0 through 2. Specifically, the determination uses instantaneousvalue err and mobile average value err_ave. Instantaneous value errindicates a difference between radio packet error rates calculated(detected) by the radio monitoring unit 46 at specified times. Mobileaverage value err_ave indicates an average of differences between radiopacket error rates detected within a specified time period including agiven time. When both values err and err_ave are small, the analysisunit 47 assumes the radio communication state to be stable (normalstate) and sets the radio communication state s to 1. In this case, therate calculation unit 25 of the transmitter 11 provides transmissionrate control (hereafter referred to as wired congestion control) inconsideration for the wired communication congestion.

There may be a case where mobile average value err_ave is small andinstantaneous value err is large. In this case, the analysis unit 47assumes the radio communication state to be a short degraded state(error state) and sets radio communication state s to 1. The ratecalculation unit 25 uses the storage unit 26 to store (save) the RTT andthe transmission rate calculated when the most recent radiocommunication state s is 0 so as to provide the wired congestioncontrol.

When radio communication state s changes from 1 to 0, the ratecalculation unit 25 assumes the transmission rate stored in the storageunit 26 with state s set to 1 to be a new transmission rate.

When mobile average value err_ave is large, the analysis unit 47 assumesradio communication state s to be a long degraded state and sets radiocommunication state s to 2. In this case, the rate calculation unit 25provides the transmission rate control appropriate to the radiocommunication state (situation).

When radio communication state s changes from 0 to 2, the ratecalculation unit 25 also uses the storage medium 26 to store the RTT andthe transmission rate calculated when the most recent radiocommunication state s is 0. When radio communication state s is restoredto 0 from 2, the rate calculation unit 25 assumes that transmission rateto be a new transmission rate.

The following describes the reason to represent radio communicationstate s using three levels, i.e., normal state, short degraded state,and long degraded state. The applicants made experiments under severalconditions using a radio LAN (e.g., a radio LAN compliant with IEEE(Institute of Electrical and Electronics Engineers) 802.11) and examinedfading occurrence and its influence. As a result, the applicants foundthat the radio communication is subject to occurrence of both a shortdegraded state of radio communication and a slightly long degraded stateof radio communication for several hundreds of milliseconds to severalseconds.

As a result of further detailed examinations, the applicants found thata long degraded state of radio communication occurs when there are manyreflective obstacles and ambient surroundings are greatly influenced byfading or when the base station 14 provides control to change atransmission mode or a coding rate.

In addition, the applicants examined an overall communication statebetween the transmitter 11 and the receiving terminal 12 to find thatthe short degraded state of radio communication usually does notimmediately influence the overall communication state and that the longdegraded state of radio communication greatly increases the RTT anddecreases the throughput. This is possibly because, when the radiocommunication contains an extra band, the buffer control of the basestation 14 may remove an influence of the momentary degraded state ofthe radio communication.

As mentioned above, the short degraded state of radio communicationdiffers from the long degraded state of radio communication ininfluences on the overall communication state between the transmitter 11and the receiving terminal 12. The transmission system 1 representsradio communication state s using three levels, i.e., the normal state,the short degraded state, and the long degraded state. The ratecalculation unit 25 provides transmission rate control according to thelevels.

State s, when set to 1, represents the short degraded state that doesnot immediately influence the overall communication state. When state sis set to 1, the rate calculation unit 25 provides the wired congestioncontrol similarly to a case where state s is set to 0 to represent thenormal state. On the other hand, state s, when set to 2, represents theradio communication's long degraded state that greatly increases the RTTand decreases the throughput. When state s is set to 2, the ratecalculation unit 25 provides the transmission rate control appropriatefor the radio communication state (situation).

Referring now to FIG. 5, the following describes a data (content)reception process performed by the receiving terminal in FIG. 2. Forexample, this data reception process starts when the reception means 42Breceives a radio wave corresponding to data transmitted from thetransmission unit 24A of the transmitter 11 via the IP network 13, thebase station 14, and the antenna 41.

At Step S1, the radio monitoring unit 46 works based on packetized datasupplied from the reception means 42B to calculate (acquire) the radiopacket error rate as an initial value and supplies it to the analysisunit 47. The analysis unit 47 stores its instantaneous value err in thestorage unit 48 and then proceeds to Step S2.

At Step S2, the analysis unit 47 determines whether or not a specifiedtime (e.g., 20 through 50 ms) has elapsed. That is, the analysis unit 47determines whether or not an interrupt is generated from a timer (notshown) that counts the time to acquire the radio packet error rate. Whenit is not determined that the specified time has elapsed, the analysisunit waits until the specified time elapses.

After Step S2, the process proceeds to Step S3. The reception detectionunit 43 works based on the packetized data supplied from the receptionmeans 42B and the time information from the timer unit 49 to acquire apacket loss rate, a sequence number, and a data reception time, andsupplies them to the analysis unit 47.

More specifically, the reception detection unit 43 works based on thepacketized data from the reception means 42B to detect (acquire) apacket loss rate for the overall communication channel and supplies itto the analysis unit 47. The reception detection unit 43 acquires thesequence number in the header information attached to the packet.Further, the reception detection unit 43 works based on the timeinformation indicative of the current time supplied from the timer unit49 to acquire the time as the data reception time and supplies thesequence number and the data reception time to the analysis unit 47.

After Step S3, the process proceeds to Step S4. The radio monitoringunit 46 works based on data supplied from the reception means 42B toacquire the radio packet error rate, supplies it to the analysis unit47, and proceeds to Step S5.

At Step S5, the analysis unit 47 calculates a difference between twovalues as instantaneous value err. One is the initial value supplied atStep S1 or the radio packet error rate supplied at the previous Step S4.The other is the radio packet error rate supplied at the most recentStep S4. The process at Step S5 may be omitted to use the radio packeterror rate from the radio monitoring unit 46 as instantaneous value errunchangedly.

After Step S5, the process proceeds to Step S6. The analysis unit 47works based on instantaneous value err calculated at Step S5 to performa radio state determination process that determines radio communicationstate s. The radio state determination process will be described indetail with reference to FIG. 6 later.

After Step S6, the process proceeds to Step S7. The analysis unit 47assumes the time currently supplied from the patent document 49 to bethe control message transmission time. Based on the control messagetransmission time and the data reception time supplied at Step S3, theanalysis unit 47 calculates time t between the control messagetransmission time and the data reception time and the proceeds to StepS8.

At Step S8, the analysis unit 47 supplies a control message to thetransmission unit 42A of the radio communication unit 42. The controlmessage contains information indicative of state s determined at StepS6, the radio packet error rate supplied at Step S4, the packet lossrate and the sequence number supplied at Step S3, and time t calculatedat Step S7. The transmission unit 42A packetizes the control message.The transmission unit 42A transmits radio wave corresponding to thepacketized control message via the antenna 41 and then returns to StepS2 to repeat the above-mentioned process. That is, the packet loss rate,the sequence number, time t, and instantaneous value err are acquiredand the control message is transmitted at every specified time.

Referring now to FIG. 6, the following describes the radio statedetermination process at Step S6 in FIG. 5.

At Step S21, the analysis unit 47 calculates mobile average valueerr_ave based on instantaneous value err calculated at the most recentStep S5 in FIG. 5 and instantaneous value err already stored in thestorage unit 48. Specifically, the analysis unit 47 calculates previousaverage value err_ave′, i.e., an average of instantaneous values err asmany as the number of most recent values (e.g., 29) out of theinstantaneous values err already stored in the storage unit 48. Theanalysis unit 47 works based on the previous average value err_ave′ andinstantaneous value err calculated at the most recent Step S5 tocalculate mobile average value err_ave using equation (1) below.err _(—) ave=□err _(—) ave′+(1−□)err  (1)

where □ is the predetermined constant (e.g., 0.9) smaller than 1.

After Step S21, the process proceeds to Step S22. The analysis unit 47uses the storage unit 48 to store instantaneous value err and mobileaverage value err_ave calculated at Step S5 in FIG. 5. When the storageunit 48 has no free area, the analysis unit 47 deletes the earliestinstantaneous value err and mobile average value err_ave.

After Step S22, the process proceeds to Step S23. The analysis unit 47determines whether or not mobile average value err_ave stored at StepS22 is smaller than predetermined threshold value Th1. When mobileaverage value err_ave is determined to be smaller than predeterminedthreshold value Th1, the process proceeds to Step S24.

At Step S24, the analysis unit 47 determines whether or notinstantaneous value err is smaller than predetermined threshold valueTh2. When instantaneous value err is determined to be smaller thanpredetermined threshold value Th2, the process proceeds to Step S25.

At Step S25, the analysis unit 47 sets radio communication state s to 0,returns Step S6 in FIG. 5, and then proceeds to Step S7.

When it is determined at Step S23 that mobile average value err_ave isnot smaller than (is greater than or equal to) predetermined thresholdvalue Th1, the process proceeds to Step S27. The analysis unit 47 setsstate s to 2, returns to Step S6 in FIG. 5, and then proceeds to StepS7.

When it is determined at Step S24 that instantaneous value err isgreater than or equal to specified threshold value Th2, the processproceeds to Step S26. The analysis unit 47 sets state s to 1, returns toStep S6 in FIG. 5, and proceeds to Step S7.

Referring now to FIG. 7, the following describes a transmission ratecalculation process performed by the rate calculation unit 25 in FIG. 2.For example, the transmission rate calculation process starts when thereception means 24B receives a control message transmitted from thereceiving terminal 12 at Step S8 in FIG. 5 via the base station 14 andthe IP network 13.

At Step S41, the rate calculation unit 25 calculates the RTT based onthe sequence number and time t in the control message supplied from thereception means 24B. Specifically, data transmission time T indicatesthe time for the transmission unit 24A to transmit data. The ratecalculation unit 25 stores data transmission time T associated with asequence number attached to that data in the storage unit 26. The ratecalculation unit 25 works based on the sequence number from thereception means 24B to read data transmission time T1 corresponding tothat sequence number from the storage unit 26. The rate calculation unit25 uses data transmission time T1, time T2 supplied from the timer unit27, and time t to calculate the RTT using equation (2) below.RTT=T2−T1−t  (2)

After Step S41, the process proceeds to Step S42. The rate calculationunit 24 stores state s of the control message from the reception means24B in the storage unit 26 and determines whether or not state s is setto 0.

When it is determined at Step S42 that state s is set to 0, the processproceeds to Step S43. The rate calculation unit 24 determines whether ornot previous state p_s, i.e., state s stored in the storage unit 26 atthe previous Step S42, is set to 0. When it is determined that previousstate p_s is not 0, the process proceeds to Step S44.

At Step S44, the rate calculation unit 24 reads the RTT and thetransmission rate saved (stored) at Step S47 (to be described) from thestorage unit 26 and proceeds to S45.

At Step S45, the rate calculation unit 24 calculates a transmission rateusing not only the read transmission rate or RTT, but also a TCPfriendly transmission rate calculation equation for wired congestioncontrol (e.g., TFRC specified in RFC3448).

Specifically, the rate calculation unit 24 assumes the read transmissionrate to be a new transmission rate as is. In this case, the ratecalculation unit 24 restores the short or long degraded state of theradio communication state s to the normal state to fast recover thetransmission rate.

The rate calculation unit 24 can calculate a transmission rate using theRTT calculated at Step S41 or the RTT read at Step S44 and the packetloss rate in the control message just supplied from the reception means24B. The transmission rate 24 can compare the calculated transmissionrate with the read transmission rate to assume a smaller transmissionrate to be the new transmission rate. In this case, the wiredcommunication congestion is taken into consideration. Due to theremaining influence of the radio communication's degraded state,however, the transmission rate may become small.

The rate calculation unit 24 supplies the transmission rate to thecoding unit 22 to terminate the process. As a result, the transmissionunit 24A transmits data at the transmission rate calculated by the ratecalculation unit 24.

When it is determined at Step S43 that previous state p_s is also set to0, the process proceeds to Step S45. According to the wired congestioncontrol technique, the rate calculation unit 24 similarly calculates aTCP friendly transmission rate using the RTT calculated at Step S41 andthe packet loss rate in the control message from the reception means24B. The rate calculation unit 24 corrects the transmission rate basedon the AIMD algorithm. The rate calculation unit 24 supplies thecorrected transmission rate to the coding unit 22.

When it is determined at Step S42 that control message's state s is notset to 0, the process proceeds to Step S46. The rate calculation unit 24determines whether or not previous state p_s is also set to 0.

When it is determined at Step S46 that previous state p_s is set to 0,the process proceeds to Step S47. The rate calculation unit 24 saves(stores) the RTT calculated at the previous Step S41 and thetransmission rate calculated at the previous Step S45 in the storageunit 26. That is, the rate calculation unit 24 saves the RTT and thetransmission rate in the normal state (state s=1) before radiocommunication state s is degraded.

When it is determined at Step S46 that previous state p_s is not 0, orafter the process at Step S47, the process proceeds to Step S48. Therate calculation unit 24 determines whether or not control message'sstate s is set to 2.

When it is determined at Step S48 that control message's state s is not2, i.e., control message's state s is 1, the rate calculation unit 24proceeds to Step S45. According to the wired congestion controltechnique, the rate calculation unit 24 calculates a transmission rateusing the RTT calculated at Step S41 and the packet loss rate in thecontrol message from the reception means 24B. The rate calculation unit24 supplies the calculated transmission rate to the coding unit 22.

When it is determined at Step S48 that state s is 2, the processproceeds to Step S49. The rate calculation unit 25 calculates reachprobability P (=1−(radio packet error rate)) based on the radio packeterror rate in the control message supplied from the reception means 24Band then proceeds to Step S50.

At Step S50, the rate calculation unit 25 multiplies reach probability Pby the transmission rate corresponding to the normal radio communicationstate saved at the most recent Step S47 to find a new transmission rate.In this manner, it is possible to calculate an available transmissionrate for the degraded radio communication state.

Referring now to FIG. 8, the following describes a data transmissionprocess for the transmitter 11 in FIG. 2 to transmit data to thereceiving terminal 12.

At Step S61, the transmission unit 24A of the transmitter 11 transmitspacketized data provided with sequence number i1 at a predeterminedtransmission rate to the receiving terminal 12 via the IP network 13 andthe base station 14. At this time, the radio communication state isassumed to be normal.

At Step S80, the receiving terminal 12 performs the process at Steps S1to S5 in FIG. 5 and the process at Steps S21 to S25 in FIG. 6 to setradio communication state s to 0 (no radio influence). The receivingterminal 12 then performs the process at Steps S7 and S8 in FIG. 5. Thereceiving terminal 12 transmits radio wave corresponding to the controlmessage containing the information indicative of sequence number i1,time t1, packet loss rate p_loss_(—)1, state s set to 0, and radiopacket error rate err_r1.

After Step S61, the process proceeds to Step S62. The reception means24B of the transmitter 11 receives the control message transmitted fromthe receiving terminal 12. The rate calculation unit 25 performs theprocess at Steps S41 to S43 and S45 in FIG. 7 and calculatestransmission rate rate1 in accordance with the wired congestion controltechnique. The rate calculation unit 25 supplies transmission rate rate1to the coding unit 22.

After Step S62, the process proceeds to Step S63. The transmission unit24A transmits data at transmission rate rate1. At this time, the radiocommunication state is assumed to be shortly (instantaneously) degraded.

After Step S80, the process proceeds to Step S81. The receiving terminal12 performs the process at Steps S2 to S5 in FIG. 5 and the process atSteps S21 to S24 in FIG. 6 and sets radio communication state s to 1(determined to be shortly degraded). The receiving terminal 12 thenperforms the process at Steps S7 and S8 in FIG. 5. The receivingterminal 12 transmits radio wave corresponding to the control messagecontaining the information indicative of sequence number i2, time t2,packet loss rate p_loss_(—)2, state s set to 1, and radio packet errorrate err_r2.

After Step S63, the process proceeds to Step S64. The reception means24B of the transmitter 11 receives the control message transmitted fromthe receiving terminal 12. The rate calculation unit 25 performs theprocess at Steps S41, S42, S46, and S47 in FIG. 7 and allows the storageunit 26 to save the RTT calculated at Step S62 (Step S41 in FIG. 7) andtransmission rate rate1 calculated at Step S62 (Step S45 in FIG. 7).

After Step S64, the process proceeds to Step S65. The rate calculationunit 25 performs the process at Steps S48 and 45 in FIG. 7. According tothe wired congestion control technique, the rate calculation unit 25calculates transmission rate rate2 using the RTT calculated at Step S64(Step S41 in FIG. 7) and control message's packet loss rate p_loss_(—)2received at Step S64. The rate calculation unit 25 supplies transmissionrate rate2 to the coding unit 22 and proceeds to Step S66.

At Step S66, the transmission unit 24A transmits data at transmissionrate rate2. At this time, the radio communication state is assumed to belong (continuously) degraded.

After Step S81, the process proceeds to Step S82. The receiving terminal12 performs the process at Steps S2 to S5 in FIG. 5 and the process atSteps S21 to S23 and S27 in FIG. 6 and sets radio communication state sto 2 (determined to be long degraded). The receiving terminal 12 thenperforms the process at Steps S7 and S8 in FIG. 5. The receivingterminal 12 transmits radio wave corresponding to the control messagecontaining the information indicative of sequence number i3, time t3,packet loss rate p_loss_(—)3, state s set to 2, and radio packet errorrate err_r3.

After Step S66, the process proceeds to Step S67. The reception means24B of the transmitter 11 receives the control message transmitted fromthe receiving terminal 12. The rate calculation unit 25 performs theprocess at Steps S41, S42, S46, and S48 to S50 in FIG. 7. Based on reachprobability P, the rate calculation unit 25 multiplies transmission raterate1 saved at Step S64 (S47 in FIG. 7) by reach probability P. The ratecalculation unit 25 assumes a resulting value to be transmission raterate3. The rate calculation unit supplies transmission rate rate3 to thecoding unit 22 and proceeds to Step S68.

At Step S68, the transmission unit 24A transmits data at transmissionrate rate3. At this time, the radio communication state is assumed to berestored to normal.

After Step S82, the process proceeds to Step S83. The receiving terminal12 performs the process at Steps S2 to S6 in FIG. 5 and the process atStep S21 to S25 in FIG. 6, and then sets radio communication state s to0 (determined to be recovered). The receiving terminal 12 then performsthe process at Steps S7 and S8 in FIG. 5. The receiving terminal 12transmits radio wave corresponding to the control message containing theinformation indicative of sequence number i4, time t4, packet loss ratep_loss_(—)4, state s set to 0, and radio packet error rate err_r4.

After Step S68, the process proceeds to Step S69. The reception means24B of the transmitter 11 receives the control message transmitted fromthe receiving terminal 12. The rate calculation unit 25 performs theprocess at Steps S41 to S43 and S44 in FIG. 7 and reads the RTT andtransmission rate nate1 that are saved at Step S64 (S47 in FIG. 7)before the radio communication state degradation. The rate calculationunit 25 performs the process at S45 in FIG. 7, assumes the readtransmission rate rate1 to be the new transmission rate, and suppliestransmission rate nate1 to the coding unit 22.

After Step S70, the process proceeds to Step S71. The transmission unit24A transmits data at transmission rate rate1.

For ease of explanation, FIG. 8 shows that the transmitter 11 receivesthe control message and then transmits data. Actually, the transmitter11 transmits data as needed without wait for reception of the controlmessage.

Referring now to FIGS. 9A through 9C, the following describestransmission rates controlled in the transmission system 1 in FIG. 2under the fading environment.

FIG. 9A shows temporal changes of radio packet error rates (%). FIG. 9Bshows temporal changes of transmission rates (Mbps). An upper part ofFIG. 9C shows temporal changes of RTT (ms). A lower part of FIG. 9Cshows temporal changes of packet loss rates (%). In FIGS. 9A through 9C,the abscissa represents time (s).

In FIG. 9A, a high radio packet error rate for one second or longeroccurs approximately at the time points of 30 through 35 seconds (circleE1 in FIG. 9A), 38 through 40 seconds (circle E2 in FIG. 9A), 45 through50 seconds (circle E3 in FIG. 9A), and 62 seconds (circle E4 in FIG.9A). That is, long degraded states of the radio communication occurapproximately at the time points of 30 through 35 seconds, 38 through 40seconds, 45 through 50 seconds, and 62 seconds.

In this case, the rate calculation unit 25 calculates reach probabilityP at Step S49 in FIG. 7 based on the radio packet error rate in thecontrol message supplied from the reception means 24B. At Step S50, therate calculation unit 25 uses reach probability P to multiply thetransmission rate saved at the most recent Step S47 before degradationof the radio communication by reach probability P to find a newtransmission rate. Accordingly, the transmission rate decreases as theradio packet error rate increases. The transmission rate increases asthe radio packet error rate decreases.

As shown in FIG. 9A, the long degraded state (circle E2 in FIG. 9A) ofradio communication s occurs approximately at the time. In this case, asshown in FIG. 9B, the transmission rate decreases as the radio packeterror rate increases. The transmission rate increases as the radiopacket error rate decreases (circle E1 in FIG. 9A). When the radiocommunication state s is long degraded, the transmission rate iscalculated based on reach probability P (throughput variation).Therefore, the rate calculation unit 25 can calculate availabletransmission rates in radio communication state s. As a result, the RTTand the packet loss rate decrease (circles G1 and H1 in FIG. 9C), makingit possible to provide a stable transmission rate.

At the time point of approximately 40 seconds in FIG. 9A, the radiocommunication's long degraded state is restored to the normal state,i.e., the radio packet error rate becomes approximately 0 (point E5 inFIG. 9A). In this case, the rate calculation unit 25 assumes thetransmission rate saved at Step S47 in FIG. 7 before degradation of theradio communication to be a new transmission rate as is. As a result,the transmission rate is restored to the one valid before the longdegradation occurs (point F2 in FIG. 9B) approximately one second oftime f1 after the radio communication's long degraded state is restoredto the normal state.

As shown in FIG. 9A, the radio communication's long degraded state (E3in FIG. 9A) occurs at the time points of 45 to 50 seconds. In this case,as shown in FIG. 9B, the transmission rate decreases as the radio packeterror rate increases. The transmission rate increases as the radiopacket error rate decreases (F3 in FIG. 9B). As a result, the RTT andthe packet loss rate decrease (circles G2 and H2 in FIG. 9).

At the time point of approximately 48 seconds in FIG. 9A, the radiocommunication's long degraded state is restored to the normal state(circle E6 in FIG. 9A). In this case, the transmission rate is restoredto the one valid before the long degradation occurs (point F4 in FIG.9B) approximately shorter than one second of time f2 after the radiocommunication's long degraded state is restored to the normal state.

As mentioned above, the rate calculation unit 25 saves the transmissionrate valid when the radio communication state is normal. When the radiocommunication state is restored to normal, the rate calculation unit 25assumes that transmission rate to be a new transmission rate. In FIGS.1A through 1C, it takes approximately two or three seconds of time b 1or approximately eight seconds of time b2 until the transmission raterecovers after the radio communication state is restored to normal. Bycontrast, the rate calculation unit 25 can immediately recover thetransmission rate after the radio communication state is restored tonormal.

As a result, the transmission system 1 in FIG. 2 shortly degrades animage corresponding to the data displayed on the output unit 45 when thetransmission rate is low (e.g., circles F1 and F2 in FIG. 9B). However,no irregular framing occurs because the RTT remains low (e.g., circlesG1 and G2 in FIG. 9B). In this manner, the transmission system 1 in FIG.2 can improve the quality of images displayed on the output unit 45 byperforming the transmission rate calculation process in FIG. 7.

FIG. 10 shows another functional construction example of thetransmission system 1 according to an embodiment.

The transmission system 1 in FIG. 10 is composed of the wired IP network13, the radio base station 14, a transmitter 81, and a receivingterminal 82. Differently from the transmission system 1 in FIG. 2, thetransmission system 1 in FIG. 10 uses the receiving terminal 82 tocalculate a transmission rate. The receiving terminal 82 transmits thistransmission rate as a control message to the transmitter 81. Themutually corresponding parts in FIGS. 10 and 2 are designated by thesame reference numerals and a detailed description is omitted forsimplicity. In the appended claims, data transmission means can beembodied by a transmission unit 91A in FIG. 10, for example; controlinformation reception means can be embodied by a reception means 91B inFIG. 10, for example; control means can be embodied by a coding unit 22in FIG. 10, for example; data reception means can be embodied by areception means 101B in FIG. 10, for example; determination means can beembodied by an analysis unit 104 in FIG. 10, for example; generationmeans can be embodied by a rate calculation unit 105 in FIG. 10, forexample; and control information transmission means can be embodied by atransmission unit 101A in FIG. 10, for example.

The transmitter 81 is composed of a content storage unit 21, a codingunit 22, a transmission control unit 23, and a communication unit 91.

The communication unit 91 is composed of a transmission unit 91A and areception means 91B. Similarly to transmission unit 24A in FIG. 2, thetransmission unit 91A transmits packetized data from the transmissioncontrol unit 23 via the IP network 13 and the base station 14. Thereception means 91B receives a transmission rate from the receivingterminal 82. The transmission rate is received as a control messageattached with a sequence number. At this time, the transmission unit 91Atransmits a response message corresponding to the control message to thereceiving terminal 82 by attaching the control message's sequence numberto the response message.

The reception means 91B receives the transmission rate transmitted as acontrol message from the antenna 41 via the IP network 13 and the basestation 14. The reception means 911B supplies the transmission rate tothe coding unit 22.

The receiving terminal 82 is composed of the antenna 41, the decodingunit 44, an output unit 45, the radio monitoring unit 46, a radiocommunication unit 101, a reception detection unit 102, a timer unit103, an analysis unit 104, a rate calculation unit 105, and a storageunit 106.

The radio communication unit 42 is composed of the transmission unit101A and the reception means 101B. The transmission unit 101A assumes atransmission rate supplied from the rate calculation unit 105 to be thecontrol message. The transmission unit 101A packetizes that controlmessage and outputs radio wave corresponding to the packetized controlmessage via the antenna 41.

The reception means 101B converts the radio wave received via theantenna 41 into data or a response message corresponding to the radiowave. The reception means 101B supplies the data to the radio monitoringunit 46 and the reception detection unit 102 and supplies the responsemessage to the reception detection unit 102.

The reception detection unit 102 detects a packet loss rate for theoverall communication channel based on the packetized data from thereception means 101B and supplies the packet loss rate to the analysisunit 47. The reception detection unit 102 acquires a sequence numberattached to the packet. The reception detection unit 102 is suppliedwith time information indicative of the current time and acquires thattime as the data reception time. The reception detection unit 102 storesthe data reception time associated with its sequence number in abuilt-in storage unit (not shown). Further, the reception detection unit102 supplies the sequence number to the analysis unit 104.

In addition, the reception detection unit 102 acquires not only thesequence number attached to the response message from the receptionmeans 101B, but also the time information indicative of the current timesupplied from the timer unit 103 as the time to receive the responsemessage (hereafter referred to as a response message reception time).The reception detection unit 102 calculates the RTT based on the storeddata reception time associated with the sequence number and the responsemessage reception time and supplies the RTT to the analysis unit 104. Inaddition, the reception detection unit 102 supplies data from thereception means 42B to the decoding unit 44.

The timer unit 103 keeps track of the current time and supplies timeinformation indicative of the current time to the reception detectionunit 102 and the rate calculation unit 105.

Similarly to the analysis unit 47 in FIG. 2, the analysis unit 104supplies the radio packet error rate from the radio monitoring unit 46to the storage unit 106 for storage. The analysis unit 104 reads theradio packet error rate already stored in the storage unit 106 anddetermines radio communication state s based on the radio packet errorrate. The analysis unit 47 supplies the rate calculation unit 105 withstate s and the radio packet error rate as well as the packet loss rate,the RTT, and the sequence number from the reception detection unit 102.

The rate calculation unit 105 calculates the transmission rate based onstate s, the radio packet error rate, the packet loss rate, and the RTT.Depending on needs, the rate calculation unit 105 supplies thecalculated transmission rate and the RTT from the analysis unit 47 tothe storage unit 104 for storage. The rate calculation unit 105 readsthe transmission rate and the RTT already stored in the storage unit104. The rate calculation unit 105 supplies the transmission unit 101Aof the radio communication unit 101 with the transmission rate attachedwith the sequence number from the analysis unit 47 as a control message.The storage unit 106 stores the radio packet error rate from theanalysis unit 104 and the transmission rate and the RTT from the ratecalculation unit 105.

Referring now to FIG. 11, the following describes a data receptionprocess performed by the receiving terminal 82 in FIG. 10. For example,the data reception process starts when the reception means 42B receivesradio wave corresponding to data from the transmission unit 24A of thetransmitter 81 via the IP network 13, the base station 14, and theantenna 41.

The process at Steps S91 and S92 is the same as the process at Steps S1and S2 in FIG. 5 and a description is omitted.

At Step S93, the reception detection unit 102 acquires the packet lossrate and the sequence number based on the packetized data supplied fromthe reception means 42B. The reception detection unit 102 acquires theRTT based on the response message supplied from the reception means 42Band the time information from the timer unit 103 and supplies them tothe analysis unit 104.

Specifically, the reception detection unit 102 acquires the packet lossrate and the sequence number attached to the packet based on thepacketized data from the reception means 42B. The reception detectionunit 102 is supplied with time information indicative of the currenttime and acquires that time as the data reception time. The receptiondetection unit 102 stores the data reception time associated with itssequence number in the built-in storage unit. Further, the receptiondetection unit 102 supplies the packet loss rate and the sequence numberto the analysis unit 104.

In addition, the reception detection unit 102 acquires not only thesequence number attached to the response message from the receptionmeans 42B, but also the time information indicative of the current timesupplied from the timer unit 103 as the response message reception time.The reception detection unit 102 calculates the RTT based on the storeddata reception time associated with the sequence number and the responsemessage reception time and supplies the RTT to the analysis unit 104.

The process at Steps S94 to S96 is the same as the process at Steps S4to S6 in FIG. 5 and a description is omitted.

After the process at Step S96, the analysis unit 47 supplies the ratecalculation unit 105 with state s determined at Step S96, the radiopacket error rate supplied at Step S94, and the packet loss rate, thesequence number, and the RTT supplied at Step S93, and then proceeds toStep S97.

At Step S97, the rate calculation unit 105 performs the process similarto that at Steps S42 to S50 in FIG. 7 using state s, the radio packeterror rate, the packet loss rate, and the RTT supplied from the analysisunit 47 to calculate a transmission rate.

After Step S97, the process proceeds to Step S98. The rate calculationunit 105 provides the transmission rate calculated at Step S97 with thesequence number supplied from the analysis unit 47 to create a controlmessage and supplies the control message to the transmission unit 101Aof the radio communication unit 101. The transmission unit 101Apacketizes the control message and transmits radio wave corresponding tothe packetized control message via the antenna 41. The process returnsto Step S92.

Referring now to FIG. 12, the following describes the data transmissionprocess for the transmitter 81 in FIG. 10 to transmit data to thereceiving terminal 82.

At Step S101 similarly to Step S61 in FIG. 8, the transmission unit 91Aof the transmitter 81 transmits data provided with sequence number i1 ata predetermined transmission rate to the receiving terminal 82 via theIP network 13 and the base station 14. At this time, the radiocommunication state is assumed to be normal.

At Step S121, the receiving terminal 82 performs the process at StepsS91 to S95 in FIG. 11 and the process at Steps S21 to S25 in FIG. 6 toset radio communication state s to 0 (no radio influence), and thenproceeds to Step S122. At Step S122, the rate calculation unit 105 ofthe receiving terminal 82 performs the process at Steps S42, S43, andS45 in FIG. 7, and calculates transmission rate rate1 according to thewired congestion control technique.

The rate calculation unit 105 performs the process at Step S98 in FIG.11, provides transmission rate rate1 with sequence number i1 suppliedfrom the analysis unit 104 to create a control message, and supplies itto the transmission unit 101A. The transmission unit 101A packetizes thecontrol message and transmits radio wave corresponding to the packetizedcontrol message to the transmitter 81 via the antenna 41.

After Step S101, the process proceeds to Step S102. The reception means91B of the transmitter 81 receives transmission rate rate1 transmittedat Step S122 as the control message from the transmission unit 101A ofthe receiving terminal 82 and supplies transmission rate rate1 to thecoding unit 22.

At this time, the transmission unit 91A transmits a response messagecorresponding to the control message received by the reception means 91Bby providing the response message with the sequence number attached tothe control message. The response message is used for calculating theRTT in the reception detection unit 102.

After Step S102, the process proceeds to Step S103. similarly to StepS63 in FIG. 8, the transmission unit 91A transmits data at transmissionrate rate1. At this time, the radio communication state is assumed to beshortly degraded.

After Step S122, the process proceeds to Step S123. The receivingterminal 12 performs the process at Steps S92 to S95 in FIG. 11 and theprocess at Steps S21 to S24 and S26 in FIG. 6 and sets radiocommunication state s to 1 (determined to be shortly degraded), and thenproceeds to Step S124.

At Step S124, the rate calculation unit 105 of the receiving terminal 82performs the process at Steps S42, S46, and S47 in FIG. 7 and allows thestorage unit 26 to save the RTT acquired at Step S123 (Step S93 in FIG.11) and transmission rate rate1 calculated at Step S122 (Step S45 inFIG. 7).

After Step S124, the process proceeds to Step S125. The rate calculationunit 105 performs the process at Steps S48 and S45 in FIG. 7. Accordingto the wired congestion control technique, the rate calculation unit 105calculates transmission rate rate2 using the RTT and the packet lossrate acquired at Step S123 (Step S93 in FIG. 11). The rate calculationunit 25 performs the process at Step S98. The rate calculation unit 25provides transmission rate rate2 with the sequence number from theanalysis unit 104 and transmits it as the control message to thetransmission unit 101A. The transmission unit 101A packetizes thecontrol message and transmits radio wave corresponding to the packetizedcontrol message.

After Step S103, the process proceeds to Step S104. The reception means91B of the transmitter 81 receives the control message transmitted fromthe transmission unit 101A of the receiving terminal 82 and supplies thecontrol message to the coding unit 22.

After Step S104, the process proceeds to Step S105. Similarly to StepS66 in FIG. 8, the transmission unit 91A transmits data at transmissionrate rate2. At this time, the radio communication state is assumed to belong degraded.

After Step S125, the process proceeds to Step S126. The receivingterminal 12 performs the process at Steps S92 to S95 in FIG. 11 and theprocess at Steps S21 to S23 and S27 in FIG. 6. The receiving terminal 12sets radio communication state s to 2 (determined to be long degraded)and then proceeds to Step S127.

At Step S127, the rate calculation unit 105 of the receiving terminal 82performs the process at Steps S42, S46, and S48 to S50 in FIG. 7. Basedon reach probability P, the rate calculation unit 105 multiplies reachprobability P by transmission rate rate1 saved at Step S124 (Step S47 inFIG. 7) to find new transmission rate rate3. The rate calculation unit25 performs the process at Step S98 in FIG. 11. The rate calculationunit 25 provides transmission rate rate3 with the sequence number fromthe analysis unit 104 and transmits it as the control message to thetransmission unit 101A. The transmission unit 101A packetizes thecontrol message and converts it into radio wave to transmission.

After Step S105, the process proceeds to Step S106. The reception means91B of the transmitter 81 receives the transmission rate transmitted atStep S127 as the control message from the transmission unit 101A of thereceiving terminal 82 and supplies the transmission rate to the codingunit 22.

After Step S106, the process proceeds to Step S107. Similarly to StepS68 in FIG. 8, the transmission unit 91A transmits data at transmissionrate rate3. At this time, the radio communication state is assumed to berestored to normal.

After Step S127, the process proceeds to Step S128. The receivingterminal 12 performs the process at Steps S92 to S95 in FIG. 11 and theprocess at Steps S21 to S25 in FIG. 6. The receiving terminal 12 setsradio communication state s to 0 (determined to be recovered) and thenproceeds to Step S129.

At Step S129, the rate calculation unit 105 performs the process atSteps S42 to S45 in FIG. 7. The rate calculation unit 105 reads the RTTand transmission rate nate1 that are saved at Step S124 (S47 in FIG. 7)before the radio communication state degradation and assumes rate1 to bethe new transmission rate. The rate calculation unit 105 performs theprocess at Step S98 in FIG. 11. The rate calculation unit 105 providestransmission rate rate1 with the sequence number and transmits it as thecontrol message to the transmission unit 101A. The transmission unit101A packetizes the control message and transmits radio wavecorresponding to the packetized control message.

After Step S107, the process proceeds to Step S108. The reception means91B of the transmitter 81 receives transmission rate rate1 transmittedat Step S129 as the control message from the transmission unit 101A ofthe receiving terminal 82 and supplies the transmission rate to thecoding unit 22.

After Step S108, the process proceeds to Step S109. similarly to StepS70 in FIG. 8, the transmission unit 91A transmits data at transmissionrate rate1.

As mentioned above, the transmission system 1 in FIG. 10 uses thereceiving terminal 82 to calculate transmission rates. It is possiblefor the transmitter 81 to save processing loads and the memory storagecapacity. Accordingly, the transmission system 1 in FIG. 10 ispreferable for a case where the transmitter 81 such as a server todeliver data simultaneously delivers (transmits) data to many receivingterminals 82.

The transmission system 1 in FIGS. 1 and 10 can be easily constructedusing the existing IP network 13 and the base station 14 without addingor changing functions of the IP network 13 and the base station 14. Thetransmission system 1 in FIGS. 1 and 10 can be also constructed usingthe sophisticated base station 14 enabling the transmitter 81 and thereceiving terminal 82 to exchange more detailed and realtime controlmessages.

When the base station 14 supplies useful parameters as the informationabout states specific to wired communication such as the controlinformation, the radio monitoring unit 46 gives no limitation on the useof the parameters and the other calculation techniques.

While the embodiment calculates transmission rates using the radiopacket error rate, it may be preferable to calculate a transmission rateusing an average of radio packet error rates.

The transmission system 1 in FIGS. 1 and 10 may be wirelessly connectedto the base station 14 instead of using the IP network 13.

Techniques for calculating The RTT for the reception detection unit 102in FIG. 10 are not limited to the above-mentioned technique of usingresponse messages.

As mentioned above, when radio communication state s is set to 2 toindicate the long degraded state, the transmission system 1 stores thetransmission rate as the information to control the data transmissionimmediately before radio communication state s is set to 2. When radiocommunication state s is afterwards set to 0 to indicate the normalstate, the transmission system 1 uses the most recently storedtransmission rate to control the data transmission. When the radiocommunication is restored to the normal state from the degraded state,the transmission system 1 can fast recover the data transmission qualitybased on the transmission control state before the degradation.

In this specification, the process steps describe a program that allowsa computer to perform various processes. The process steps need not bealways chronologically processed in the order described in the flowchartand may include processes that are concurrently or individually (e.g.,parallel processes or object-oriented processes).

The program may be processed by one computer or multiple computers in adistributed fashion. Further, the program may be transferred to a remotecomputer for execution.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A transmitting and receiving system comprising a transmittingapparatus to transmit data and a receiving apparatus to receive the databy means of radio communication, wherein the transmitting apparatuscomprises: data transmission means for transmitting the data; stateinformation reception means for receiving state information from thereceiving apparatus, wherein the state information is indicative ofstates of the radio communication; and control means for controllingtransmission using the data transmission means; wherein, when the stateinformation reception means receives state information indicating adegraded state of the radio communication, the control means storescontrol information for the data transmission means to controltransmission immediately before the state information is received; and,when the state information reception means thereafter receives stateinformation indicating a normal state of the radio communication, thecontrol means uses the most recently stored control information tocontrol transmission by means of the data transmission means; andwherein the receiving apparatus comprises: data reception means forreceiving data transmitted from the data transmission means by means ofthe radio communication; determination means for determining the radiocommunication state based on data received by the data reception means;and state information transmission means for transmitting stateinformation to the transmitting apparatus indicating the radiocommunication state determined by the determination means.
 2. Atransmitting apparatus to transmit data to a receiving apparatus, saidtransmitting apparatus comprising: data transmission means fortransmitting the data; state information reception means for receivingstate information from the receiving apparatus, wherein the stateinformation is indicative of states of the radio communication; andcontrol means for controlling transmission using the data transmissionmeans, wherein, when the state information reception means receivesstate information indicating a degraded state of the radiocommunication, the control means stores control information for the datatransmission means to control transmission immediately before the stateinformation is received; and, when the state information reception meansthereafter receives state information indicating a normal state of theradio communication, the control means uses the most recently storedcontrol information to control transmission by means of the datatransmission means.
 3. The transmitting apparatus according to claim 2,wherein the state information reception means receives state informationrepresenting any one of a long degraded state, a short degraded state,and a normal state of the radio communication, and wherein, when thestate information reception means receives state information indicatinga long degraded state of the radio communication, the control meanscontrols transmission corresponding to a degraded state of the radiocommunication.
 4. The transmitting apparatus according to claim 2,wherein the control information concerns a transmission rate, andwherein, when the state information reception means receives stateinformation indicating a degraded state and then state informationindicating a normal state, the control means controls transmission ofthe data transmission means so that the data is transmitted at atransmission rate calculated based on the most recently storedtransmission rate.
 5. The transmitting apparatus according to claim 4,wherein the control information further contains information of RoundTrip Time (RTT), and wherein, when the state information reception meansreceives state information indicating a degraded state and then stateinformation indicating a normal state, the control means controlstransmission of the data transmission means so that the data istransmitted at a transmission rate calculated based on the most recentlystored transmission rate and RTT.
 6. A method of transmitting data froma transmitting apparatus to transmit data to a receiving apparatuscomprising: transmitting the data; receiving state informationindicating the radio communication state from the receiving apparatus;and controlling transmission according to a process of the datatransmission step, wherein, when a process at the state informationreception step receives state information indicating a degraded state ofthe radio communication, a process at the control step stores controlinformation for controlling transmission according to a process at thedata transmission step immediately before reception of the stateinformation and, when the state information reception step thereafterreceives state information indicating a normal state of the radiocommunication, the process at the control step uses the most recentlystored control information to control transmission according to theprocess at the data transmission step.
 7. A program stored on a computerreadable medium and allowing a computer to perform a process to transmitdata to a receiving apparatus, the program comprising: transmitting thedata; receiving state information indicating the radio communicationstate from the receiving apparatus; and controlling transmissionaccording to a process of the data transmission step, wherein, when aprocess at the state information reception step receives stateinformation indicating a degraded state of the radio communication, aprocess at the control step stores control information for controllingtransmission according to a process at the data transmission stepimmediately before reception of the state information and, when thestate information reception step thereafter receives state informationindicating a normal state of the radio communication, the process at thecontrol step uses the most recently stored control information tocontrol transmission according to the process at the data transmissionstep.
 8. A receiving apparatus to receive data by means of radiocommunication from a transmitting apparatus that transmits the data, thereceiving apparatus comprising: data reception means for receiving datatransmitted from the transmitting apparatus by means of the radiocommunication; determination means for determining the radiocommunication state based on data received by the data reception means;and state information transmission means for transmitting stateinformation indicating the radio communication state determined by thedetermination means to the transmitting apparatus.
 9. The receivingapparatus according to claim 8, wherein the determination meansdetermines the radio communication state based on whether the datareceived corresponds to any of a long degraded state, a short degradedstate, and a normal state.
 10. The receiving apparatus according toclaim 9 further comprising: detection means for detecting radiocommunication information about the radio communication state based onthe data, wherein the determination means determines the radiocommunication state based on a value for the radio communication statedetected by the detection means at a specified time and an average ofvalues for the radio communication information detected within aspecified time period including said specified time.
 11. A method for areceiving apparatus to receive data by means of radio communication froma transmitting apparatus that transmits the data, the method comprising:receiving data transmitted from the transmitting apparatus by means ofthe radio communication; determining the radio communication state basedon data received by a process at the data reception step; andtransmitting state information indicating the radio communication statedetermined by a process at the determination step to the transmittingapparatus.
 12. A program stored on a computer readable medium and forallowing a computer to perform a process of receiving data from atransmitting apparatus to transmit the data by means of radiocommunication, the program comprising: receiving data transmitted fromthe transmitting apparatus by means of the radio communication;determining the radio communication state based on data received by aprocess at the data reception means; and transmitting state informationindicating the radio communication state determined by a process at thedetermination step to the transmitting apparatus.
 13. A transmitting andreceiving system having a transmitting apparatus for transmitting dataand a receiving apparatus for receiving the data by means of radiocommunication, wherein the transmitting apparatus comprises: datatransmission means for transmitting the data; control informationreception means for receiving control information to controltransmission performed by the data transmission means; and control meansfor controlling transmission performed by the data transmission meansbased on control information received by the control informationreception means, wherein the receiving apparatus comprises: datareception means for receiving data transmitted from the datatransmission means by means of the radio communication; determinationmeans for determining the radio communication state based on datareceived by the data reception means; generation means for generatingthe control information based on the radio communication statedetermined by the determination means; and control informationtransmission means for transmitting control information generated by thegeneration means to the transmitting apparatus, wherein, when thedetermination means determines the radio communication state to bedegraded, the generation means stores the most recently generatedcontrol information and, when the determination means thereafterdetermines the radio communication state to be normal, uses the mostrecently generated control information to generate the controlinformation.
 14. A transmitting apparatus for transmitting data to areceiving apparatus by means of radio communication, the transmittingapparatus comprising: data transmission means for transmitting the data;control information reception means for receiving control informationwhich is transmitted from the receiving apparatus based on a radiocommunication state and is used to control transmission performed by thedata transmission means; and control means for controlling transmissionperformed by the data transmission means based on control informationreceived by the control information reception means.
 15. A transmittingmethod for transmitting data from a transmitting apparatus to areceiving apparatus comprising: transmitting the data; receiving controlinformation which is transmitted from the receiving apparatus based onthe radio communication state and which is used to control transmissionaccording to a process at the data transmission step; and controllingtransmission according to a process of the data transmission step basedon control information received by a process at the control informationreception step.
 16. A program stored on a computer readable medium forallowing a computer to perform a process to transmit data to a receivingapparatus, the program comprising: transmitting the data; receivingcontrol information which is transmitted from the receiving apparatusbased on the radio communication state and which is used to controltransmission according to a process at the data transmission step; andcontrolling transmission according to a process of the data transmissionstep based on control information received by a process at the controlinformation reception step.
 17. A receiving apparatus for receiving databy means of radio communication from a transmitting apparatus whichtransmits the data, the receiving apparatus comprising: data receptionmeans for receiving data transmitted from the transmitting apparatus bymeans of the radio communication; determination means for determining aradio communication state based on data received by the data receptionmeans; and generation means for generating control information tocontrol transmission performed by the transmitting apparatus based onthe radio communication state determined by the determination means; andcontrol information transmission means for transmitting controlinformation generated by the generation means to the transmittingapparatus, wherein, when the determination means determines the radiocommunication state to be degraded, the generation means stores the mostrecently generated control information and, when the determination meansthereafter determines the radio communication state to be normal, thegeneration means uses the most recently generated control information togenerate the control information
 18. The receiving apparatus accordingto claim 17, wherein the determination means determines, based on thedata, that the radio communication state corresponds to any of a longdegraded state, a short degraded state, and the normal state.
 19. Thereceiving apparatus according to claim 18, wherein, when thedetermination means determines the radio communication state to be longdegraded, the generation means generates the control informationcorresponding to the radio communication state's long degraded state.20. The receiving apparatus according to claim 17 further comprising:detection means for detecting radio communication information about theradio communication based on the data, wherein the determination meansdetermines the radio communication state based on a value for the radiocommunication state detected by the detection means at a specified timeand an average of values for the radio communication informationdetected within a specified time period including the specified time.21. The receiving apparatus according to claim 17, wherein the controlinformation concerns a transmission rate; and wherein, when thedetermination means determines a change in the radio communication statefrom degraded to normal, the generation means generates controlinformation based on the most recently stored transmission rate.
 22. Thereceiving apparatus according to claim 21, wherein the controlinformation further contains information of Round Trip Time (RTT); andwherein, when the determination means determines a change in the radiocommunication state from degraded to normal, the generation meansgenerates control information based on the most recently storedtransmission rate and RTT.
 23. A method for a receiving apparatus toreceive data by means of radio communication from a transmittingapparatus which transmit the data, the method comprising: receiving datatransmitted from the transmitting apparatus by means of the radiocommunication; determining the radio communication state based on datareceived by a process at the data reception means; generating controlinformation to control transmission performed by the transmittingapparatus based on the radio communication state determined by a processat the determination step; and transmitting control informationgenerated by a process at the generation step to the transmittingapparatus, wherein, when a process at the determination step determinesthe radio communication state to be degraded, a process at thegeneration step stores the most recently generated control informationand, when a process at the determination step thereafter determines theradio communication state to be normal, a process at the generation stepuses the most recently generated control information to generate thecontrol information.
 24. A program stored on a computer readable mediumfor allowing a computer to perform a process of receiving data from atransmitting apparatus thus transmit the data by means of radiocommunication, the program comprising: receiving data transmitted fromthe transmitting apparatus by means of the radio communication;determining the radio communication state based on data received by aprocess at the data reception means; generating control information tocontrol transmission performed by the transmitting apparatus based onthe radio communication state determined by a process at thedetermination step; and transmitting control information generated by aprocess at the generation step to the transmitting apparatus, wherein,when a process at the determination step determines the radiocommunication state to be degraded, a process at the generation stepstores the most recently generated control information and, when aprocess at the determination step thereafter determines the radiocommunication state to be normal, a process at the generation step usesthe most recently generated control information to generate the controlinformation.